三道英语单选题 在线等！说明原因！

Question

1.I shall never forget the days —— we stayed together on the farm。
A that B which C when D why

2.Mother has bought all —— is necessary for New Year‘s Day。
A what B which C that D because

3.My hometown isn’t —— it used to be ten years ago。
A what B who C where D which

Answer 1

c the days 在从句中做时间状语
c 先行词是不定代词 只能用that
表语从句，。。。。的样子，选a